Drive device and drive method of display panel
In a drive device of a display panel, a write operation (Ws, We) for writing display data into a frame memory and a read operation (a, a′ to h, h′) for reading the display data written in the frame memory are performed. An implementation start timing a of the read operation is set to be after an implementation start timing Ws of the write operation, and an implementation end timing a′ of the read operation is set to be upon or after an implementation end timing We of the write operation. The read operation is performed a plurality of times during one frame period.
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1. Field of the Invention
The present invention relates to a drive device and a drive method of a display panel in which tearing generated by allowing write timing of display data for an image memory to get ahead of read timing can be prevented in a drive device of a display panel in which light-emission control of a display panel is implemented employing one frame image memory.
2. Description of the Related Art
In an image display device adopted in a relatively small terminal equipment, for example, such as a cellular telephone, a PDA (Personal Digital Assistant), and the like, from the viewpoint of cost, power consumption, parts mounting space, and the like, a structure provided with one screen (one frame) image memory (frame memory) is adopted.
In order to implement a display operation of an image using the above-described structure, a write operation in which display data is written in a frame memory and a read operation in which the display data is read out of the frame memory are performed during the same one frame period.
In a display device in which gradation control is performed by dividing one frame period into a plurality of subframes, the read operation is implemented a plurality of times during the same frame period. In this case, due to the influence of the vestige of the analog gradation method in which the so-called cathode-ray tube or the like is employed, and due to reasons that the drive frequency of an IC is suppressed, the read operation is implemented a plurality of times while the write operation is implemented during the entire one frame period.
The read operation from the frame memory is also implemented a plurality of times during one frame period as shown by reference characters a to h in
In order to prevent the above trouble, Japanese Patent Application Laid-Open No. S62-11889 proposes that an image memory of two screens is used so that write timing and read timing of display data are controlled so as not to generate the above overtaking. Further, Japanese Patent Application Laid-Open No. H10-161842 proposes means for simplifying write timing and read timing of display data, utilizing an image memory of two screens or more.
However, in the structures disclosed in the above-described Japanese Patent Application Laid-Open No. S62-11889 and Japanese Patent Application Laid-Open No. H10-161842, an image memory of at least two screens has to be prepared, so that image display devices such as the cellular telephone and PDA have a problem that such structures are hard to be adopted due to cost and the like.
Meanwhile, in this type of display device, by having PLE (Peak Luminance Enhancement) control means by which an Average Picture Level (APL) of a video signal to be displayed is found in order to control display intensity in the display device by this average picture level, it is expected that low power consumption of the display device can be realized.
In this PLE control, for example, the average picture level (APL) of the video signal which corresponds to entire one frame screen is detected, and based on this average picture level, a display intensity level that is an intensity level for actually performing image display is set.
In this case, in the PLE control, in a case where the average picture level is low (in a case where an entire image is dark) even though a video signal has the same intensity level, a display intensity level is set to a high level so that high intensity display is executed. On the other hand, in a case where average picture level is high (in a case where an entire image is bright), a display intensity level is set to a low level so that power consumption is suppressed. In this manner, the PLE control is performed so that low power consumption can be realized and that an image having an excellent contrast can be displayed.
As described above, a display device provided with the PLE control means by which the average picture level APL of a video signal to be displayed is found and in which the display intensity is controlled by this APL is shown in the following Japanese Patent Application Laid-Open No. H9-281927 and Japanese Patent Application Laid-Open No. 2001-175220 and the like.
Meanwhile, in the PLE control also, in the case where the APL is computed utilizing one frame memory, the APL is computed based on display data of one frame which is one frame earlier than said frame, and according to the result thereof, control of the intensity of the next frame is performed so that a drift of one frame occurs even though the calculation result of the APL value is reflected in the intensity control.
Further, as already described, in the display device in which gradation control is performed by dividing one frame period into a plurality of subframes, a drift of one subframe occurs even though the calculation result of the APL value is reflected in the intensity control. That is, as shown in
Similarly, when an APL value is calculated in the timing starting from, for example, reference character b, the PLE control is realized in a subframe which starts from the next reference character c. As a result, since the APL is calculated based on data in which data of one earlier frame (old frame) and data of a new frame are mixed, there is a problem that calculation result of APL is not accurate.
SUMMARY OF THE INVENTIONThe present invention has been developed, paying attention to the above problem, and it is a first object of the present invention to provide a drive device and a drive method of a display panel in which the tearing can be prevented from being generated while a small capacity video memory is utilized.
Further, it is a second object of the present invention to provide a drive device and a drive method of a display panel in which the tearing can be prevented from being generated while a small capacity video memory is utilized, and in which based on a calculated value of the APL which is based on data of one frame to be displayed, the PLE control of this frame can be realized.
A drive device of a display panel according to the present invention which has been developed in order to resolve the first problem is a drive device of a display panel in which a write operation for writing display data into a frame memory and a read operation for reading the display data written in the frame memory are performed during one frame period, and is constructed such that an implementation start timing of the read operation is set to be after an implementation start timing of the write operation, such that an implementation end timing of the read operation is set to be upon or after an implementation end timing of the write operation, and such that the read operation is performed a plurality of times during one frame period.
Further, a drive device of a display panel according to the present invention which has been developed in order to resolve the second problem is the drive device of the display panel which is constructed such that an APL operation in which a mean intensity level of display data written in the frame memory is calculated is performed at least one time during one frame period in addition to the above-described structure.
A drive method of a display panel according to the present invention which has been developed in order to resolve the first problem is a drive method of a display panel in which a write operation for writing display data into a frame memory and a read operation for reading the display data written in the frame memory are performed during one frame period, characterized in that an implementation start timing of the read operation is set to be after an implementation start timing of the write operation, in that an implementation end timing of the read operation is set to be upon or after an implementation end timing of the write operation, and in that the read operation is performed a plurality of times during one frame period.
Further, a drive method of a display panel according to the present invention which has been developed in order to resolve the second problem is the drive method of the display panel, characterized in that an APL operation in which a mean intensity level of display data written in the frame memory is calculated is performed at least one time during one frame period in addition to the above-described drive method.
A drive device of a display panel according to the present invention will be described below based on embodiments shown in
In
The embodiment shown in this
The light emission control circuit 11 operates to generate a synchronization signal for a scan driver 21, a data driver 22, and an erase driver 23 in the video display means B based on the horizontal and vertical synchronization signals in the video signal.
The A/D converter circuit 12 samples the inputted analog signal based on the clock signal CK supplied from the light emission control circuit 11, and operates to convert this to display data for each pixel to supply this to the video memory 13. The video memory 13 operates to write respective display data supplied from the A/D converter circuit 12 sequentially in the video memory 13 by the write control signal W supplied from the light emission control circuit 11.
The video memory 13 functions as a frame memory in which display data of one frame can be written. That is, by the write operation, data of one screen (one frame) in a later-written display panel is written, and thereafter display data of next one frame is rewritten sequentially to be stored (overwritten).
At the same time as this, display data written in the video memory (hereinafter referred to also as frame memory) 13 is sequentially read out of the memory 13 by the read control signal R supplied from the light emission control circuit 11, and the image thereof is displayed on the display panel in a state in which display control by a subframe method and intensity control by PLE are received as described later herein.
The light emission control circuit 11 reads display data written in the frame memory 13 in synchronization with respective subframe periods which will be described later herein, and supplies a display data signal to the data driver 22. The light emission control circuit 11 also operates to calculate APL from display data written in the frame memory 13. In this case, the APL is obtained by calculating, from display data written in the frame memory 13, pixels, intensity, and the rate of gradation value (light-emission rate) regarding which light emission control is performed in a later-described display panel 31. Therefore, the light emission control circuit 11 also performs a function as light-emission rate calculating means.
Further, the light emission control circuit 11 operates to refer to the intensity setting table 14 based on the calculated light-emission rate to implement a PLE operation. In this PLE operation, the light emission control circuit 11 operates to refer to the intensity setting table 14 based on the light-emission rate to generate an appropriate control signal for the data driver 22 and the erase driver 23 constituting the video display means B. Operations of the data driver 22 and the erase driver 23 at this time will be described later in detail.
Next, reference numeral 31 in the video display means B shows a display panel in which a large number of pixels 32 each of which contains an organic EL element are arranged in a matrix pattern. In this display panel 31, a scan line 33, a data line 34, and an erase signal line 35 which are connected to the above-described scan driver 21, the data driver 22, and the erase driver 23, respectively, are arranged, and at these intersecting points the pixels 32 including the EL elements are arranged, respectively. The display panel 31 is constructed in such a way that a pixel light-emission drive voltage is supplied from a power supply circuit 24 to the respective pixels 32 via a power supply line 36.
A scan signal Select (referred to also as a write pulse) is supplied to the gate of the data write transistor Tr1 via the scan line 33 connected to the scan driver 21. The drain of the data write transistor Tr1 is connected to the gate of a light-emission drive TFT, that is, a light-emission drive transistor Tr2 and to one terminal of a charge-retaining capacitor C1.
The source of the light-emission drive transistor Tr2 is connected to the other terminal of the capacitor C1, and is constructed such that a drive voltage Vcc is supplied to the source via the power supply line 36. The drain of the light-emission drive transistor Tr2 is connected to the anode terminal of the organic EL element E1, and the cathode terminal of this organic EL element E1 is connected to a reference potential (ground).
Further, an erase signal Erase (referred to also as an erase pulse) is supplied from the erase driver to the gate of an erase transistor Tr3 as an erase TFT via the erase signal line 35. The source and drain of the erase transistor Tr3 are connected to both ends of the capacitor C1, respectively.
In the circuit configuration of the pixels 32 shown in
In the structure of the pixels 32 shown in
When applying of the write pulse for the gate of the control transistor Tr1 is stopped, the transistor Tr1 is so-called cut-off. However, the gate voltage of the drive transistor Tr2 is maintained by stored charges in the capacitor C1, and thus drive current to EL element E1 is maintained. Accordingly, EL element E1 can continue a light-emitting state corresponding to the data signal Vdata during a period until a next address operation (one subframe period later described).
Meanwhile, during a light-emitting period of the EL element E1 (during one subframe period), the erase pulse Erase by which the erase transistor Tr3 is turned on is supplied from the erase driver 23. Thus, charges charged in the capacitor C1 can be erased (discharged) instantaneously. As a result, the drive transistor Tr2 is in a cut-off state, and the EL element E1 is extinguished immediately. In other words, by controlling the output timing of the erase pulse Erase from the erase driver 23, the light-emitting period in one frame of the EL element E1 is controlled, so that predetermined gamma characteristics and dimmer characteristics can be realized.
That is, the example shown in
In
Here, in a case where the light-emission rate of the pixels is low (in other words, a case where the APL is low), the light-emission control shown in FIG. 5[a] is executed, and in a case where the light-emission rate of the pixels is high (a case where the APL is high), the light-emission control shown in
In
Here, for example, in a case where gradation “8” is to be realized, a series of light-emission patterns shown in FIG. 5[a] or FIG. 5[b] are executed for pixels during one frame period. Further, for example, in a case where gradation “5” is to be realized, the light-emission drive operation is executed during SF1 to SF4 shown in FIG. 5[a] or FIG. 5[b], and all of the following respective subframe periods SF5 to SF7 are in an extinction state. Thus, a light emission intensity in accordance with the total of the light-emitting periods of the pixels during one frame period can be obtained.
The erase pulse shown in
In the intensity setting table 14, light-emitting periods for respective subframes are stored as parameters, corresponding to the light-emission rate. When a subframe number whose light-emission control should be implemented is supplied from the subframe counter 15 to the logical processing unit 16, the logical processing unit 16 accesses the table 14 and operates to generate an output timing signal of the erase pulse based on the parameters of light-emitting periods stored in accordance with the subframe number.
This is generated as the output timing signal of the erase pulse for each subframe respectively in response to the light-emission rate of the pixels as shown in
This can be realized by allowing the operation of the A/D converter circuit 12 shown in
The implementation start of a first read operation of the display data during the one frame period is implemented at the timing shown by reference character a, and the implementation end of its read operation is implemented at the timing shown by reference character a′. In this manner, the implementation start timing a of the read operation is set to be after the implementation start timing Ws of the write operation, and the implementation end timing a′ of the read operation is set to be upon or after the implementation end timing We of the write operation. Following that, the read operation is implemented a plurality of times during one frame period as shown by b, b′ to h, h′.
That is, the number of times of the implementation of the read operation of the display data corresponds to the number of subframes. Operation is performed such that the display data read out of the frame memory 13 a plurality of times is supplied from the light emission control circuit 11 shown in
The write and read operations of the display data shown in
Next,
In the example shown in
Operation is performed such that the display data read out of the frame memory 13 a plurality of times is supplied from the light emission control circuit 11 shown in
The write and read operations of the display data shown in
In the example shown in
A first read operation of the display data is implemented at the timing shown by reference character a in
As shown in
The APL value calculated during the period of the reference characters A, A′ is employed for the PLE control during one frame period. The PLE control utilizing the APL value is as already described with reference to
By the APL calculation operation performed at the timing shown in
In the example shown in this
Accordingly, in the example shown in this
Claims
1. A drive device of a display panel in which a write operation for writing display data into a frame memory and a read operation for reading the display data written in the frame memory are performed during one frame period, characterized in that
- an implementation start timing of the read operation is set to be after an implementation start timing of the write operation, and in that
- an implementation end timing of the read operation is set to be upon or after an implementation end timing of the write operation,
- wherein the read operation is performed a plurality of times during one frame period.
2. The drive device of the display panel according to claim 1, wherein a plurality of subframes exist in one frame period.
3. The drive device of the display panel according to claim 2, wherein the number of times of the implementation of the read operation corresponds to the number of the subframes.
4. The drive device of the display panel according to any one of claims 1 to 3, wherein an APL operation in which a mean intensity level of display data written in the frame memory is calculated is performed at least one time during one frame period.
5. The drive device of the display panel according to claim 4, wherein the implementation start timing of the APL calculation operation is set to be upon or after the implementation start timing of the write operation and prior to the implementation start timing of the read operation, and wherein the implementation end timing of the APL calculation operation is set to be upon or after the implementation end timing of the write operation and upon or before the implementation start timing of the read operation.
6. The drive device of the display panel according to claim 4, wherein the APL calculation operation is performed at the same time as the write operation.
7. The drive device of the display panel according to any one of claims 1 to 3, wherein a display operation for displaying an image on the display panel is performed at the timing in synchronization with the read operation.
8. The drive device of the display panel according to claim 4, wherein a display operation for displaying an image on the display panel is performed at the timing in synchronization with the read operation.
9. The drive device of the display panel according to claim 5, wherein a display operation for displaying an image on the display panel is performed at the timing in synchronization with the read operation.
10. The drive device of the display panel according to claim 6, wherein a display operation for displaying an image on the display panel is performed at the timing in synchronization with the read operation.
11. A drive method of a display panel in which a write operation for writing display data into a frame memory and a read operation for reading the display data written in the frame memory are performed during one frame period, characterized in that
- an implementation start timing of the read operation is set to be after an implementation start timing of the write operation, and in that
- an implementation end timing of the read operation is set to be upon or after an implementation end timing of the write operation,
- wherein the read operation is performed a plurality of times during one frame period.
12. The drive method of the display panel according to claim 10, wherein a plurality of subframes exist in one frame period.
13. The drive method of the display panel according to claim 11, wherein the number of times of the implementation of the read operation corresponds to the number of the subframes.
14. The drive method of the display panel according to claim 10, wherein an APL operation in which a mean intensity level of display data written in the frame memory is calculated is performed at least one time during one frame period.
15. The drive method of the display panel according to claim 13, wherein the implementation start timing of the APL calculation operation is set to be upon or after the implementation start timing of the write operation and is prior to the implementation start timing of the read operation, and wherein the implementation end timing of the APL calculation operation is set to be upon or after the implementation end of the write operation and upon or before the implementation start timing of the read operation.
16. The drive method of the display panel according to claim 13, wherein the APL calculation operation is performed at the same time as the write operation.
17. The drive method of the display panel according to claim 10, wherein a display operation for displaying an image on the display panel is performed at the timing in synchronization with the read operation.
18. The drive method of the display panel according to claim 13, wherein a display operation for displaying an image on the display panel is performed at the timing in synchronization with the read operation.
19. The drive method of the display panel according to claim 14, wherein a display operation for displaying an image on the display panel is performed at the timing in synchronization with the read operation.
20. The drive method of the display panel according to claim 15, wherein a display operation for displaying an image on the display panel is performed at the timing in synchronization with the read operation.
Type: Application
Filed: Jan 18, 2007
Publication Date: Sep 13, 2007
Applicant: TOHOKU PIONEER CORPORATION (Yamagata)
Inventors: Masaki Murakata (Yonezawa-shi), Shuichi Seki (Yonezawa-shi)
Application Number: 11/654,554